In the conventional method, the gasification of biomass is done by heating the biomass with a controlled air supply to produce a mixture of hydrogen and carbon monoxide. This mixture is combustible and can be burnt as a source of energy.
Alternatively, many waste materials such as cow dung, sewage, spent wash or other effluents, are microbially converted into a combustible mixture of methane and carbon dioxide that can be used as an energy source. This conversion involves the stages of hydrolysis of biomass, its conversion into short chain fatty acids and their further conversion into a mixture of methane and carbon dioxide. The three stages of conversion, each brought about microbiologically, are invariably brought about using a single reactor, although in rare cases, the third stage is separated from the first two. The waste materials are utilized as and when available and the conversion is primarily aimed at reducing the polluting load in an economical manner. In case of cow dung the presently operated single stage system is ideally designed for domestic use in rural areas.